»6 . THE CONS T RUC T ION OF TIMBER
P L A T E gravings ; but it is the mere deception of the eye, viewing a tliicicnefs of the Pith in
' which a great many beds of the Blebs are feen together, lying over one another.
Fig. 6. There is no difference in the form of one Bleb and another j and we have feen at Fig. 6.
what one Bleb is. Its membrane is fmiple, and its outhne is Cngle; but here the
outlines of many Blebs are feen one over another, and variouily interfering one the
other.
I t has been the cuftom to view fuch a flice of the Pith as could be cut off thin
with a razor J but the raoft careful way of executing this takes in many cCurfes of
thefe Blebs. In a Üice cut to one thoufandth part of an inch" by the engine here
figured, a great part of this deception vaniihes, bccaufe very few beds of the Blebs
are taken : and in one of the fifteen hundredth part of an inch, (for the inftrument
will afford fuch) the whole error vaniihes. We fee the thing as it is; one firaple ar-
F'g- 7- rangement of cut Blebs. Such a piece is reprefented at Fig. 7.
W i t h refpefí of thofe other figures fuppofed to exift in the Pi t h of Trees and Plants,
I have fometimes exemplified their appearance by the ftruflure of a piece of gauze;
which, tho' compofed only of ftrait lines, perpendicular and horizontal j that is
forming fimple fquares; yet if it be laid double, a new arrangement of lines appears >
and if again doubled, yet another; and fo on, till, at fix times doubled, the variety
is in a manner endlefs. The difference of figures cannot be more between the appearances
of the Pith of different trees, all made by fimple circles, than in thefe which
ourfelves have formed of fimple fquares.
A piece of the Pith of Sweet-briar, cut in the ufual way, is reprefented at
Plate X * a: this being much thicker than the flice at Plate X, 5, and 7, affords a
multitude of confus'd faint forms, which in the Figure 6. being of a thinner piece
more magnify'd, are feen to arife foleiy from the way in which they lie under one
another. .
Thus ends the examination of the feveral conftituent parts of Timber. Thefe are
a l l : They are effential; for they are found in all kinds and they are here reprefented
as they have appeared, in repeated obfervations, to the Author, to his noble Patron
and to many afiemblies of philofophic friends. Nothing is enlarged, nothing altered
from what the fight received in thofe feveral views: if in any part that has been yet
deceived, let it not be imputed to purpofed mifreprefentation. Nothing is feigned :
if in any thing he has e r red; Reader! thou art a man, and pardon human frailiy.
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